1. Field of the Invention
The present invention relates to Compton light sources, and more specifically, it relates to the use of ultra-narrow bandwidth (10E-3 or lower) and high beam flux quasi-mono-energetic x-rays and gamma rays for determining isotopic content of materials.
2. Description of Related Art
Mono-Energetic Gamma-rays (MEGa-rays) can be used to efficiently excite nuclear resonances (so called Nuclear Resonance Fluorescence or NRF) that are unique isotopic signatures of all materials. By monitoring the absorption of resonant photons from a MEGa-ray beam, one may rapidly determine the presence or absence of specific isotopes in an object and with the appropriate detector one may also determine the absolute amount of that isotope present. Furthermore, because most NRF resonances are in the 1 MeV to 3 MeV spectral range, this evaluation can be accomplished on thick (meter scale) objects if sufficiently high flux MEGa-ray beams are employed. As discussed infra, beams of mono-energetic gamma-rays can be produced by Thomson (or more precisely Compton) scattering of short duration laser pulses off of relativistic bunches of electrons. The output of these laser-based MEGa-ray sources are collimated, directional, polarized, extremely bright and tunable via adjustment of either the laser color or the electron beam energy. As discussed infra, the detection of the narrow band resonant gamma-ray absorption can be accomplished with a dual isotope notch observation (DINO) detector.
U.S. Pat. No. 7,564,241, titled “Isotopic Imaging Via Nuclear Resonance Fluorescence with Laser-Based Thomson Radiation,” filed Sep. 26, 2006, incorporated herein by reference, teaches laser-based gamma-ray sources based on Compton scattering and further teaches their use for the isotope-specific detection of materials. U.S. patent application Ser. No. 12/506,639, titled “Dual isotope Notch Observer for Isotope Identification, Assay and Imaging with Mono-Energetic Gamma-Ray Sources,” filed Jul. 21, 2009, incorporated herein by reference, teaches a mono-energetic gamma-ray detection technology that can be used in conjunction with a laser-based gamma-ray source to accurately detect and assay the isotopic content of a material. This technology is sometimes referred to as the Dual Isotope Notch Detector (DINO).
U.S. patent application Ser. No. 13/552,610, now, U.S. Pat. No. 8,934,608, titled “High Flux, Narrow Bandwidth Compton Light Sources Via Extended Laser-Electron Interactions,” filed Jul. 18, 2012, incorporated herein by reference teaches means for producing high flux beams of bright, tunable, polarized quasi-monoenergetic x-rays or gamma-rays via laser-Compton scattering x-ray or gamma-ray. An electron source generates a train of spaced electron bunches and an RF linear accelerator accelerated the electron bunches into a laser-electron beam interaction region. The transit time of each of the accelerated electron bunches through the laser-electron beam interaction region is both greater than the duration of the accelerated electron bunch and greater than the spacing between electron hunches. A laser system is adapted to produce a laser pulse having a duration at least as long as a transit time of the laser pulse through the laser-electron beam interaction region. The laser system is arranged so that the laser pulse traverses the laser-electron beam interaction region to interact with all of the accelerated electron bunches of the train. In some embodiments, the duration of the laser pulse is substantially equal to at least a total length of the train of spaced electron bunches so that a single pass of the laser pulse through the laser-electron beam interaction region interacts with all of the accelerated electron bunches of the train. In other embodiments, the duration of the laser pulse is substantially equal to a sub-multiple of a total length of the train of spaced electron bunches. The laser system is arranged to recirculate the laser pulse through the laser-electron beam interaction region for a predetermined number of passes equal to an inverse of the sub-multiple. The spacing frequency of the electron bunches can the same as or correlated to the RF frequency of the RF linear accelerator so that an electron bunch is present for every cycle of said RF frequency.
It is desirable to utilize ultra-narrow bandwidth (10E-3 or lower) and high beam flux quasi-mono-energetic x-rays and gamma rays to determine the flow rate and/or sort materials according to isotopic content.